A resin containing magnetic material that achieves its electromagnetic characteristics by dispersing magnetic powder in a resin is used to constitute the mold core material employed in electronic parts in which specific electromagnetic characteristics are required, such as choke coils, inductors, rotary transformers, EMI elements and the like in the known art. Magnetic particles constituting such a magnetic powder are formed in an almost spherical shape to assure a sufficient degree of fluidity during injection molding.
The resin containing magnetic material described above achieves outstanding advantages such as superior dimensional accuracy and a greater degree of freedom afforded in shape since it is achieved without undergoing a sintering process, compared to magnetic oxide materials that are achieved as sintered bodies through molding and sintering. However, the electromagnetic characteristics achieved in a magnetic molded article constituted of a resin containing magnetic material obtained through the prior art technology are inferior.
For instance, if a ferrite resin achieving good injection moldability and a high degree of magnetic permeability, which is obtained by selecting an appropriate particle size distribution and an appropriate content of the ferrite powder in the ferrite resin as disclosed in Japanese Unexamined Patent Publication No. 163236/1994, is employed to constitute a magnetic molded article, a low initial magnetic permeability .mu.i of approximately 22 is achieved.
In Japanese Unexamined Patent Publication No. 204027/1994, an approach in which a heat treatment is implemented at varying temperatures for different particle sizes of magnetic particles mixed in a magnetic oxide material, is disclosed. However, the resulting magnetic molded article only achieves an initial magnetic permeability .mu.i of approximately 35 at best.
While other prior art technologies such as those disclosed in Japanese Unexamined Patent Publication No. 185540/1990, Japanese Unexamined Patent Publication No. 226799/1990, Japanese Unexamined Patent Publication No. 96202/1991, Japanese Unexamined Patent Publication No. 12029/1992, Japanese Examined Patent Publication No. 52422/1991, Japanese Unexamined Patent Publication No. 84648/1994 and the like are known, a sufficient initial magnetic permeability cannot be achieved in any of the resulting magnetic molded articles, since the dimensions of the particles mixed in the magnetic oxide material are too small, the ratio at which they are mixed is too low.